1. Field of the Invention
The present invention relates to a sensor unit and an image display apparatus having the sensor unit.
2. Description of the Related Art
As a technique to provide a high-resolution image projection apparatus using a display device, such as an LCD, having a limited number of pixels, a wobbling technique is known which uses a polarization rotation liquid crystal cell and a birefringent plate in combination to perform pixel shifts.
With the wobbling technique, the timing of shifting light is dependent upon on and off of the polarization rotation liquid crystal cell. For this reason, to provide good display, it is important to drive control the polarization rotation liquid crystal cell taking its response into consideration. For example, JP-A No. 11-296135 (KOKAI) discloses a technique to determine an ideal drive signal of the polarization rotation liquid crystal cell. The response characteristic of the polarization rotation liquid crystal cell is temperature dependent. Thus, in order to apply an ideal drive signal to the liquid crystal cell even with temperature changed, a method has also been proposed by which the drive signal is changed on the basis of temperature information from a temperature sensor (see JP-A No. 11-326877 (KOKAI)).
With the proposal described in JP-A No. 11-326877, however, the temperature of the polarization rotation liquid crystal cell is measured; therefore, its response characteristic cannot be obtained. For this reason, it is required to determine the temperature versus response characteristic relationship of the polarization rotation liquid crystal cell in advance. However, it is not practical in terms of time and cost to determine in advance the temperature versus response characteristic relationship for all the polarization rotation liquid crystal cells actually manufactured. One might suggest a method to determine the temperature versus response characteristic relationship of a reference polarization rotation liquid crystal cell in advance. However, an ideal drive signal could not be obtained because the characteristic of the reference polarization rotation liquid crystal cell is not identical to those of polarization rotation liquid crystal cells actually manufactured.
JP-A No. 2000-284255 (KOKAI) discloses a method to calculate the temperature of a display liquid crystal panel from its response speed. However, this proposal does not relate to a polarization rotation liquid crystal cell for wobbling but relates to only a liquid crystal cell for display. In addition, to measure the temperature of the liquid crystal panel, its response speed is merely measured.
As described above, the wobbling technique is known as a technique to obtain a high-resolution image projector. Heretofore, it has been difficult to provide ideal driving of a polarization rotation liquid crystal cell taking its response characteristic into consideration.
The object of the present invention is to provide a sensor unit and an image display apparatus which allow the response characteristic of a polarization rotation liquid crystal cell to be obtained exactly.